Systemic hypertension in the Okamoto-Kyoto Wistar strain of rats has been proposed as a model of human essential hypertension. Progressive persistent blood pressure elevation in these animals is accompanied by substantial cardiac hypertrophy and central hemodynamic alterations. To date, no studies of the discrete mechanical properties of hypertrophic heart muscle have been carried out in this interesting animal model. Pharmacologic intervention can delay the onset and/or lower the elevated blood pressure levels. Therefore the relationship between the offset of systolic stress and the rate and extent of recovery of myocardial mechanical alterations can be studied without multiple surgical interventions. Furthermore the relationship of age to the development and regression of hypertrophy can be assessed. A normotensive in-bred strain of Wistar stock is available as a control population. Systemic blood pressure levels can be monitored via an indirect tail method. The left ventricular columnae carneae muscle is suitable for isolated mechanical studies. Characteristics of both the active and passive components of the muscle will be analyzed in terms of force, velocity and elasticity. The development of a quantitative relationship between abnormally elevated systemic blood pressure, hypertrophying cardiac muscle, and myocardial mechanical properties is of major importance in understanding the cardiac complications of systemic hypertension. Furthermore an optimal approach to therapy of the cardiac complications will depend on an assessment of the effect of treatment on the discrete properties of hypertrophic myocardial tissue.